1. Field of the Invention
This invention relates to cooling fans and more particularly relates to detecting fan rotation direction in electronic devices.
2. Description of the Related Art
Electronic devices generate heat when in operation. Integrated circuits, resistors, and other components in electronic devices generate heat while operating. Some integrated circuits generate much more heat than other components. For example, switching elements in a switching power supply that constantly switch on and off at a fixed switching frequency typically generate a lot of heat compared to other components in the power supply. Central processing units (“CPUs”) also generate a lot of heat. Other integrated circuits may also generate more heat than surrounding components. Even where an electronic device does not have one or more specific components that generate excessive heat, general heat generation within an electronic device may be excessive.
Integrated circuits and other components that generate heat run the risk of being damaged if the temperature of the integrated circuits and components increases above designed limits. Excess heat often causes failures of electronic devices and may decrease the useful life of the electronic devices.
One solution to reduce heat buildup in electronic devices is to use one or more cooling fans. Cooling fans draw air across heat generating devices and act to carry heat away from the heat generating devices. Typically air exterior to an electronic device is at a lower temperature than air surrounding a heat generating device in an electronic device. The exterior air is drawn by a cooling fan into the electronic device and the heated air around the heat generating component is expelled from the electronic device.
Typically a cooling fan is used to pull air through the electronic device and push heated air to the exterior of the electronic device. This creates a slight vacuum compared to air pressure exterior to the electronic device and is typically more efficient than a fan that pushes exterior air into an electronic device, which may increase air pressure within the electronic device with respect to air exterior to the electronic device. Some electronic devices include more than one cooling fan. Some electronic device may include two or more fans that draw air from the electronic device and push the air to the exterior. In other electronic devices, one or more fans positioned at an air intake push air into the electronic device while one or more other fans positioned at an air exhaust pull the air from the electronic device and push the heated air to the outside.
A major problem facing electronic device manufacturers is that fans can be connected incorrectly so that a fan incorrectly connected can push air into the electronic device instead of pulling air from the electronic device as designed. This can cause an increased pressure instead of a vacuum so that cooling provided by the fan is less efficient than designed. In this case, the electronic device may overheat. Often failed electronic devices are returned to an electronic equipment manufacturer where the cause of the failures is a fan connected incorrectly. The failed equipment may be returned with “no defect found” or “NDF” because system diagnostic circuits and software in the electronic device cannot detect a fan spinning the wrong way. A fan spinning the wrong way draws power at a level close to the same fan connected so the fan spins in a correct direction; so a reversed connection typically cannot be detected by sensing fan power.
In addition, electronic devices with a fan connected incorrectly may take a long time to fail so that many electronic devices with incorrectly connected fans may be shipped before the problem is detected. Physically determining if a fan is incorrectly detected at a factory of an equipment manufacturer may also be expensive due to the time taken by employees to check the fan rotation.
Other fan direction detection methods may use some type of air pressure detectors, air flow direction sensors, and the like. Each of these methods requires specialized equipment that may increase cost of production of the electronic devices significantly.